If you’re over about 20 and learned about evolution in your high-school biology class, it’s likely that there were a number of things that didn’t seem to add up, and that you were exhorted to just take on faith. Random mutations occur, and across millions of births, the story goes, every once in a while an individual ends up with a mutation that confers a benefit for reproduction, or at least for living long enough to reproduce. The classic example is white-bodied moths (Biston betularia) on the trunk of a tree with white bark—they blend in and so are more difficult for predators to pick off. After the industrial revolution...